In Traditional Chinese Medicine (TCM), Xu chang Qing belongs to the 'Herbs that dispel Wind and Dampness' category. These herbs typically help treat what's called 'bi pain' (i.e. painful obstruction) in TCM. This roughly corresponds to arthritic and rheumatic conditions with pain, stiffness and numbness of the bones, joints and muscles.
Furthermore Xu chang Qing is Warm in nature. This means that Xu chang Qing tends to help people who have too much 'Cold' in their body, although with less effect than a plant that would be Hot in nature. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Cold in their body are said to either have a Yin Excess (because Yin is Cold in nature) or a Yang Deficiency (Yang is Hot in Nature). Depending on your condition Xu chang Qing can help restore a harmonious balance between Yin and Yang.
Xu chang Qing also tastes Pungent. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Pungent ingredients like Xu chang Qing tends to promote the circulations of Qi and Body Fluids. That's why for instance someone tends to sweat a lot when they eat spicy/pungent food.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Xu chang Qing is thought to target the Stomach and the Liver. In TCM the Stomach is responsible for receiving and ripening ingested food and fluids. It is also tasked with descending the digested elements downwards to the Small Intestine. The Liver on the other hand is often referred as the body's "general" because it is in charge of regulating the movements of Qi and the Body Fluids. It also takes a leading role in balancing our emotions.